Direct broadcast systems use various orbital slots, which correspond to different services including video and audio programming. Additional new services are continuously being offered for direct satellite broadcast system users. Typically when new services are offered existing direct satellite broadcast system components need to be replaced or altered to accommodate for the new services. The services are broadcasted via radio waves within the direct broadcast system.
In DBS systems both RHCP signals and LHCP signals are used to double the bandwidth of the transmitted signals and increase the capacity of the satellite. Typical direct broadcast systems include a direct broadcast receiver for receiving direct broadcast signals. The direct broadcast receiver includes a low noise block (LNB) or a series of individual separate LNBs. The LNB(s) may be directly connected to an integrated receiver and decoder (IRD) or may be connected to an external switching box followed by the IRD. The LNB(s) receive, combine, and amplify the RHCP signal and the LHCP signal. A program channel is selected on the IRD, which in turn may directly receive a direct broadcast signal having a particular frequency corresponding to the program channel from a particular LNB or may use the external switching box to switch to a different LNB. Each individual LNB is wired in parallel to the external switching box. Therefore, each additional LNB increases complexity and the number of components involved in production of the direct broadcast receiver.
Now referring to FIG. 1, a schematic view of a typical low noise block (LNB) 10 of a conventional direct broadcast receiver is shown. The LNB 10 receives broadcast signals having a RHCP signal 12 and a LHCP signal 14 through LNA 16 and LNA 18 respectively. The RHCP signal 12 and the LHCP signal 14 are 22 KHz or DC bias induced by a switching block 20. The RHCP signal 12 and the LHCP signal 14 are transferred from the LNAs 16, 18 to a power combiner circuit 22, which combines the RHCP signal 12 and the LHCP signal 14 to form a combined signal 24. The combined signal 24 is amplified by a radio frequency (RF) amplifier 26. After amplification the combined signal 24 is differentiated by a mixer 28 and an oscillator 30 to form an intermediate frequency (IF) signal 32. The oscillator 30 feeding the mixer 28 usually has a frequency of about 11.25 GHz. Conventional direct broadcast receivers having more than one LNB have different frequency components for each LNB corresponding to each different service. The differential between the broadcast signal frequencies and the frequency of the oscillator 30 provides the frequency of the intermediate signal 32. With the bandwidth of the broadcast signals being 500 MHz, the output intermediate frequency for the LNB(s) is usually in the range of 950–1450 MHz. The IF signal 32 is amplified by an IF amplifier 34 and transferred to the IRD. The IF signals are more conductive to transmission by means of a less expensive transmission wire or conduit, such as a simple coaxial cable.
Another LNB that has been considered for use in direct broadcast receivers, is a stacked LNB. The stacked LNB decodes a LHCP signal and a RHCP signal simultaneously. A direct broadcast receiver using stacked LNB uses one LNB for the lower frequency range of 950–1450 MHz and another LNB for a higher frequency range of 1525–2050 MHz. Either the LHCP signal or the RHCP signal is shifted from the lower frequency range to the higher frequency range so as to decode both simultaneously. The use of stacked LNB allows a direct broadcast receiver to facilitate more than two IRDs by signal splitting using an appropriately rated splitter.
New direct broadcast services are continually being offered resulting in new orbital slots. In order to accommodate for the new orbital slots the existing ODUs and the IRDs are typically replaced or altered. The replacement of the ODUs and IRDs is costly and time consuming. Therefore, it is desirable to develop a direct broadcast system that is able to accommodate for new services without the need for changing components within the direct broadcast system.
It would also be desirable to minimize the number of components within a direct broadcast system while maintaining the ability to switch between multiple LNBs, reduce wiring requirements for signal distribution, and thereby reducing costs.